Laser-assisted positron-impact ionization of atomic hydrogen in the second Born approximation

We study positron-impact ionization of atomic hydrogen in the presence of a linearly polarized laser field in the second Born approximation. The state of the fast incident positron is described by the Volkov wave function and the dressed state of the ejected electron and ground-state hydrogen are treated as a first-order time-dependent perturbative wave function. We calculate the triple differential cross section in the Ehrhardt asymmetric geometry, and numerical results indicate that the second-order effects are significant. Compared with the ionization process by electrons, the influence of the projectile charge sign appears: the binary peaks are greatly enhanced for positrons in the second Born approximation.